A computer network is a collection of interconnected computing devices that can exchange data and share resources. In a packet-based network, the computing devices communicate data by dividing the data into small blocks called packets, which are individually routed across the network from a source device to a destination device. The destination device extracts the data from the packets and assembles the data into its original form. Dividing the data into packets enables the source device to resend only those individual packets that may be lost during transmission.
Computer networks may have parallel data paths. For example, a network may have a number of interconnected intermediate devices that provide connectivity from an inbound edge router to an outbound edge router. Similarly, a communication device within a computer network may have multiple internal data paths. For example, a network router may have multiple forwarding engines to forward packets between input interfaces and output interfaces. As a result, some of the packets traveling between two locations may make use of one path, while other packets may make use of one or more alternate paths.
The sequence in which a device receives the packets may be important. For instance, a device may need to receive the packets in the sequence the source device sent the packets. Example applications that require in-sequence delivery include support of the Asynchronous Transfer Mode (ATM) over router networks, link emulation using the Internet Protocol (IP) or the Multiprotocol Label Switching (MPLS) protocol, and High-Level Data Link Control (HDLC) over IP or MPLS. Traffic may arrive out of order if packets belonging to the same packet flow are communicated using alternate paths. Further, the traffic may not be distributed evenly among the paths, which may result in congestion on one data path and unused bandwidth on another. This may decrease the efficiency of the network and increase packet latency.